during a solar storm could expose passengers to
radiation levels equivalent to the annual working
limit for air crews. This threat has left satellite
companies, aircraft operators and power companies
monitoring the solar cycle for clues as to when the
threat level will be at its highest.
By counting sunspots on the Sun’s surface
scientists have for some time known of 11-year
cycles of increasing and decreasing solar activity
and surface eruptions, driven by the tangling
and untangling of the magnetic field lines. These
plots indicate we are approaching the latest solar
minimum, and therefore entering a new cycle.
Recent magnetic field evolution models
developed by the Center of Excellence in Space
Sciences in India concluded that the solar
maximum of the next cycle, solar cycle 25, will
occur around 2024. They also suggested the
cycle could buck a wider trend of decreasing solar
maximum intensities since the early 1990s, though
perhaps not in a way that would greatly threaten
ground- or space-based infrastructure.
“It is unlikely that this will affect big solar storms,
as these can happen at any stage of the solar
cycle,” says Scott. However, anticipating the timing
and severity of the coming solar cycle could help
us prepare for the more local effects such solar
variability that effect our lives and which have only
come to light in the last decade or two.
Researcher Pablo Mauas has published a series of
papers analysing river f lows of the Paraná River, aswell as measuring snow accumulation and counting
tree rings to establish a remarkable agreement
between local precipitation rates and the number of
sunspots, tracked back over many decades. “I can
quite believe there is an 11-year cycle in the f low
rates of the river,“ says Scott, who points to evidence
of similar solar-inf luenced systems closer to home.
During recent low periods of solar activity it
seems the jet streams become more meandering,
and you get more ‘blocking events’ where air-
pressure systems get stuck over a certain location.
These phenomena are thought to account for
some of the very cold recent winters in northwest
Europe, but perhaps this trend may reverse slightly
if the next solar cycle is more active, as the Indian
research team suggests.
In his own research Scott has shown that fast
jets of solar wind passing the Earth, associated
with more active solar periods, can result in a
substantial increase in lightning strikes across
Europe for up to 40 days as a result of disturbances
to the electrical properties of the atmosphere. While
communities and populations may need to adapt to
changes in these localised weather systems, a better
way of predicting larger scale solar weather on a
more detailed day-to-day basis is an urgent priority.
This becomes more pressing if Carrington events
prove to be more common than that ‘once-in-a-
century’ tag. Reanalysis of magnetic behaviour
measurements in the Earth’s atmosphere by Scott’s
colleague Mike Lockwood has found storms inSun